The present invention relates to a liquid toner concentration detecting device which detects the concentration of solid particles in liquid toner used in a developing process for an image carrier with an electrostatic latent image formed on a photosensitive layer, as well as an image forming apparatus and a method of controlling concentration which utilize the detecting device.
An electronic photographic type image forming apparatus includes a liquid toner including a liquid carrier such as an organic solvent, silicon oil, mineral oil or edible oil in which microscopic toner resin particles containing a pigment have been dispersed.
In the electronic photographic type image forming apparatus using the liquid toner, a laser beam is scanned over the surface of an image carrier such as a photoreceptor, to form an electrostatic latent image, and the electrostatic latent image is developed by a liquid toner containing toner and a liquid carrier mixed at a predetermined ratio, thus forming a toner image.
A liquid toner developing device is configured as follows. That is, in order to form a high quality image, the concentration of toner particles in the liquid toner is measured and, in the event that the concentration of toner particles decreases due to the developing process, the concentration of toner in the liquid toner is maintained within a predetermined range by replenishing the concentrated liquid which has a high concentration of toner particles.
According to JP-A-2001-356608, a liquid toner concentration detecting device is disclosed in which a detecting head is disposed inside a tank storing a liquid toner, the detecting head is connected to a light emitter and a light receiver by means of fiber cables, the light emitted by the light emitter is injected into the liquid toner through the injection aperture of the detecting head, one part of the injected light is dispersed by the toner particles in the liquid toner, injected into the light receiving aperture of the detecting head, and received by the receiver, and the concentration of the liquid toner is detected according to the amount of the received light.
Furthermore, according to JP-A-2001-5300, a liquid toner concentration detecting device is disclosed in which a housing is disposed in liquid toner supplier which is connected to a liquid toner storage tank and a developer, and the housing is provided with liquid toner oil film forming means which forms a film of liquid toner oil inside the housing, a light source unit which emits colored light, of a wavelength of relatively low light transmissivity vis-à-vis a selected color liquid toner, to the liquid toner oil film of the selected color liquid toner, and a light detector which receives the light transmitted through the liquid toner oil film from the light source unit.
In recent years, in response to requests for compact image forming apparatuses which the users themselves can install and move as they wish within the office, and for a higher quality of output image, there has been a demand for the introduction to the office of image forming apparatuses which utilize liquid toner, which have toner particles of a smaller diameter than those of dry toner, to obtain high quality images. In meeting these demands, it can be predicted that the image forming apparatus will be subjected to tilting and vibration when being installed or moved. For this reason, in the case of the liquid toner concentration detecting device disclosed according to JP-A-2001-5300, if the image forming apparatus is tilted when installed or moved, or is subjected to vibration, there is a danger of losing the required detection accuracy due to liquid toner adhering to the light detector itself or to a detecting window disposed in the front of the light detector. Furthermore, in the case of the liquid toner concentration detecting device disclosed according to JP-A-2001-356608, in some cases it can be predicted that the volume of liquid toner in the tank decreases below a predetermined volume, the detecting head is exposed making detection impossible, or that the liquid toner adhering to the tip of the exposed detecting head will harden, so that the detecting function will not be restored even if the liquid toner is replenished.
Furthermore, in the case of the image forming apparatus using a liquid toner including a liquid carrier in which microscopic toner resin particles containing a pigment have been dispersed, in some cases, a large number of toner resin particles are consumed when forming a photographic image, and a large amount of liquid carrier is consumed when forming letter images, meaning that in order to obtain a high quality image, it is essential to constantly maintain the mixture ratio of the toner resin particles and the liquid carrier at a substantially fixed level.